<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        div{
            width: 200px;
            height: 200px;
            background-color: red;
            border-radius: 100px;
        }
    </style>
</head>

<body>
    <input type="button" value="变宽" id="btn">
    <div id="dv"></div>
    <script src="common.js"></script>
    <script>
        my$("btn").onclick = function () {
            var width = 200;
            var timeId = setInterval(function () {
                width += 10;
                if (width == 1000) {
                    clearInterval(timeId);
                }
                my$("dv").style.width = width + "px";
            }, 30)
        }
    </script>
</body>

</html>